An image-forming device can form an image at an image formation position on a recording medium, which deviates from the right position due to a physical shock from the outside or another cause, for example. For this reason, some conventional image-forming devices have a function for correcting the deviation of the image formation position based on a test pattern. Responsive to a test instruction, such image-forming device forms a test pattern for registration on a belt which drives rotationally to transfer recording medium. Then, the image-forming device detects the position of the pattern formed on the belt with an optical sensor or another device, and corrects the image formation position based on the result of the detection. After that, responsive to an image forming instruction, the image-forming device forms an image at the corrected image formation position.
Japanese unexamined patent application publication No. 2001-228670 describes that variation in the temperature of the inside of the image-forming device affects the image formation position. Especially, the fixing unit is the major cause of the variation in the inner temperature of the image-forming device. Thus, the image-forming device described in Japanese unexamined patent application publication No. 2001-228670 forms a pattern at the time when a predetermined time has elapsed since the fixing unit had been turned on. Then, the image-forming device detects the pattern and corrects the image formation position based on the result of the detection.
In addition, Japanese unexamined patent application publication No. HEI11-231750 discloses an image-forming device that obtains information of the position of a pattern and the temperature of the inside of the apparatus at a predetermined timing, and substitutes the obtained information and temperature into a predetermined function to calculate a position deviation amount that occurs after a predetermined time period has elapsed.